Omnivore

An omnivore /ˈɒmnivɔər/ is an animal whose species normally derives its energy and nutrients from a diet consisting of a variety of food sources that may include plants, animals, algae, fungi and bacteria.^[1]

The term means 'all-eater' (Latin, omnes, omnia, meaning "all" or "everything" and vorare meaning "to devour"),

Omnivores are often opportunistic, general feeders that lack carnivore or herbivore specializations for acquiring or processing food, but which nevertheless consume both animals and plants.^[2]

Etymology

The word "omnivore" is a term of convenience, and its significance varies according to the context of the type and degree of omnivory. Traditionally the definition for omnivory relies on a species "including both animal and vegetable tissue in the diet".^[3] The taxonomic utility of this definition is limited, since the diet, behavior, and phylogeny of one omnivorous species might be very different from that of another: for instance an omnivorous pig digging for roots and scavenging for fruit and carrion is taxonomically and ecologically quite distinct from an omnivorous chameleon that eats leaves and insects. The term "omnivory" is also not comprehensive because it does not deal with mineral foods such as salt licks.

Challenges for classifying

Though Carnivora is a taxon for species classification, no such equivalent exists for omnivores, as omnivores are widespread across multiple taxonomic clades. The Carnivora order does not include all carnivorous species, and not all species within the Carnivora taxon are carnivorous:^[4] the eating of flesh is phylogenetically widespread.

Many species are difficult to classify as either omnivores, herbivores, or carnivores because few animals are strictly limited to just one type of tissue in the diet. Even the cat and weasel families, usually regarded as obligate carnivores, eat a little vegetable matter, for instance when they eat the guts of prey, although this does not prove that they derive nutrition from it. Only certain species like parasitoidal insects and insects that are specialist sap-suckers can be easily classified based on their nutrient source. Another problem with classifying species as omnivore, herbivore, or carnivore concerns changes in eating habits through an animal's life cycle. Certain species, such as some grazing waterfowls like geese, are known to eat mainly animal tissue at one stage of their lives, and plant matter at another.^[5] The same is true for many insects, such as beetles in the family Meloidae,^[6] which begin by eating animal tissue as larvae, but change to plant matter after they mature. Likewise, many mosquito species begin with plants or assorted detritus. As they mature, however, the males continue to eat plant matter and nectar, but the females (such as those of Anopheles, Aedes and Culex), in addition to nectar, also eat blood in order to reproduce effectively.

Omnivorous species

General

Although cases exist of carnivores eating plant matter and herbivores eating meat, the classification "omnivore" refers to the adaptations and main food source of the species in general, so these exceptions do not make either individual animals or the species as a whole omnivorous. For the concept of "omnivore" to be regarded as a scientific classification, some clear set of measurable and relevant criteria would need to be considered to differentiate between an "omnivore" and other categories, e.g. faunivore, folivore, and scavenger.^[7] Some researchers argue that evolution of any species from herbivory to carnivory or carnivory to herbivory would be rare except via an intermediate stage of omnivory.^[8]

Omnivorous mammals

Various mammals are omnivorous in the wild, such as species of pigs,^[9] badgers, bears, coatis, hedgehogs, opossums, skunks, sloths, squirrels,^[10] raccoons, chipmunks,^[11] mice,^[12] and rats.^[13] Hominidae, including humans and chimpanzees, are omnivores,^[2][14][15] but some regard them to be anatomical herbivores who have opportunistically adapted to eating some meat.^[16][17][18]

Most bear species are omnivores

Most bear species are omnivores,^[19] but individual diets can range from almost exclusively herbivorous to almost exclusively carnivorous, depending on what food sources are available locally and seasonally. Polar bears are classified as carnivores, both taxonomically (they are in the order Carnivora), and behaviorally (they subsist on a largely carnivorous diet). Depending on the species of bear, there is generally a preference for one class of food, as plants and animals are digested differently. Wolf subspecies (including wolves, dogs, dingoes, and coyotes) have a general preference and are evolutionarily geared towards meat, but also will voluntarily eat plant material like fruits, vegetables, and grasses, and can live on such indefinitely. Also, the maned wolf is a canid whose diet is naturally 50% plant matter.

While most mammals may display "omnivorous" behavior patterns depending on conditions of supply, culture, season and so on, they will generally prefer a particular class of food, to which their digestive processes are adapted. Like most arboreal species, most squirrels are primarily granivores, subsisting on nuts and seeds.^[20] But like virtually all mammals, squirrels avidly consume some animal food when it becomes available. For example, the American Eastern gray squirrel has been introduced by humans to parts of Britain, continental Europe and South Africa. Where it flourishes, its effect on populations of nesting birds is often serious, largely because of consumption of eggs and nestlings.^[21][22]

Other species

Various birds are omnivorous, with diets varying from berries and nectar to insects, worms, fish, and small rodents. Examples include cassowaries, chickens, crows^[23] and related corvids, keas, rallidae, and rheas. In addition, some lizards, turtles, fish (such as piranhas and catfish), and invertebrates are also omnivorous.

Quite often, mainly herbivorous creatures will eagerly eat small quantities of animal food when it becomes available. Although this is trivial most of the time, omnivorous or herbivorous birds, such as sparrows, often will feed their chicks insects while food is most needed for growth.^[24] On close inspection it appears that nectar-feeding birds such as sunbirds rely on the ants and other insects that they find in flowers, not for a richer supply of protein, but for essential nutrients such as Cyanocobalamin that are absent from nectar. Similarly, monkeys of many species eat maggoty fruit, sometimes in clear preference to sound fruit.^[25] When to refer to such animals as omnivorous, or otherwise, is a question of context and emphasis, rather than of definition.

See also

References

Modelling ecosystems – trophic components General Abiotic component Abiotic stress Behaviour Biogeochemical cycle Biomass Biotic component Biotic stress Carrying capacity Competition Ecosystem Ecosystem ecology Ecosystem model Keystone species List of feeding behaviours Metabolic theory of ecology Productivity Resource Producers Autotrophs Chemosynthesis Chemotrophs Foundation species Mixotrophs Myco-heterotrophy Mycotroph Organotrophs Photoheterotrophs Photosynthesis Photosynthetic efficiency Phototrophs Primary nutritional groups Primary production Consumers Apex predator Bacterivore Carnivores Chemoorganotroph Foraging Generalist and specialist species Intraguild predation Herbivores Heterotroph Heterotrophic nutrition Insectivore Mesopredator release hypothesis Omnivores Optimal foraging theory Predation Prey switching Decomposers Chemoorganoheterotrophy Decomposition Detritivores Detritus Microorganisms Archaea Bacteriophage Environmental microbiology Lithoautotroph Lithotrophy Microbial cooperation Microbial ecology Microbial food web Microbial intelligence Microbial loop Microbial mat Microbial metabolism Phage ecology Food webs Biomagnification Ecological efficiency Ecological pyramid Energy flow Food chain Trophic level Example webs Cold seeps Hydrothermal vents Intertidal Kelp forests Lakes North Pacific Subtropical Gyre Rivers San Francisco Estuary Soil Tide pool Processes Ascendency Bioaccumulation Cascade effect Climax community Competitive exclusion principle Consumer-resource systems Copiotrophs Dominance Ecological network Ecological succession Energy quality Energy Systems Language f-ratio Feed conversion ratio Feeding frenzy Mesotrophic soil Nutrient cycle Oligotroph Paradox of the plankton Trophic cascade Trophic mutualism Trophic state index Defense/counter Animal coloration Antipredator adaptations Camouflage Deimatic behaviour Herbivore adaptations to plant defense Mimicry Plant defense against herbivory Predator avoidance in schooling fish

Modelling ecosystems – other components Population ecology Abundance Allee effect Depensation Ecological yield Effective population size Intraspecific competition Logistic function Malthusian growth model Maximum sustainable yield Overpopulation in wild animals Overexploitation Population cycle Population dynamics Population modeling Population size Predator–prey equations Recruitment Resilience Small population size Stability Species Biodiversity Density-dependent inhibition Ecological effects of biodiversity Ecological extinction Endemic species Flagship species Gradient analysis Indicator species Introduced species Invasive species Latitudinal gradients in species diversity Minimum viable population Neutral theory Occupancy-abundance relationship Population viability analysis Priority effect Rapoport's rule Relative abundance distribution Relative species abundance Species diversity Species homogeneity Species richness Species distribution Species-area curve Umbrella species Species interaction Antibiosis Biological interaction Commensalism Community ecology Ecological facilitation Interspecific competition Mutualism Storage effect Spatial ecology Biogeography Cross-boundary subsidy Ecocline Ecotone Ecotype Disturbance Edge effects Foster's rule Habitat fragmentation Ideal free distribution Intermediate Disturbance Hypothesis Island biogeography Landscape ecology Landscape epidemiology Landscape limnology Metapopulation Patch dynamics r/K selection theory Source–sink dynamics Niche Ecological niche Ecological trap Ecosystem engineer Environmental niche modelling Guild Habitat Marine habitats Limiting similarity Niche apportionment models Niche construction Niche differentiation Other networks Assembly rules Bateman's principle Bioluminescence Ecological collapse Ecological debt Ecological deficit Ecological energetics Ecological indicator Ecological threshold Ecosystem diversity Emergence Extinction debt Kleiber's law Liebig's law of the minimum Marginal value theorem Thorson's rule Xerosere Other Allometry Alternative stable state Balance of nature Biological data visualization Constructal theory Ecocline Ecological economics Ecological footprint Ecological forecasting Ecological humanities Ecological stoichiometry Ecopath Ecosystem based fisheries Endolith Evolutionary ecology Functional ecology Industrial ecology Macroecology Microecosystem Natural environment Regime shift Systems ecology Theoretical ecology List of ecology topics

Feeding behaviours Carnivores adult Hematophagy Insectivore Lepidophagy Man-eater Molluscivore Mucophagy Myrmecophagy Ophiophagy Piscivore Avivore Spongivore Vermivore Herpetivore reproductive Oophagy Paedophagy Placentophagy Breastfeeding Weaning cannibalistic Cannibalism Human cannibalism Self-cannibalism Sexual cannibalism Herbivores Folivore Frugivore Graminivore Granivore Nectarivore Palynivore Xylophagy Osteophagy Cellular Phagocytosis Myzocytosis Others Bacterivore Fungivore Coprophagia Detritivore Geophagy Omnivore Planktivore Xenophagy Methods Ambush predator Apex predator Bait balls Bottom feeding Browsing Feeding frenzy Filter feeding Grazing Hypercarnivore Hypocarnivore Intraguild predation Kleptoparasitism Lunge feeding Pivot feeding Ram feeding Scavenging Suction feeding Trophallaxis Predation Antipredator adaptation Carnivorous plant Carnivorous fungus Carnivorous protist Category:Eating behaviors